In the United States, digital television signals can be broadcast using either of two technical standards. The first is MPEG 2 which is mandatory. The second is PSIP which is an optional standard that supports enhanced features. The PSIP standard provides the ability to associate multiple channel frequencies with a single broadcaster for display in the channel guide. The MPEG 2 digital video broadcast standard provides no such capability. For MPEG 2, the major channel displayed in the program guide corresponds directly with the physical channel number (frequency) used to broadcast the digital television signal. For PSIP broadcasts, programming can be broadcast on multiple frequencies yet displayed as a collection of major and minor channels in the program guide for ease of selection by the user. That is, for PSIP, a virtual channel number can represent the physical channel carrying the broadcast whereas in MPEG 2, the concept of a virtual channel does not exist—the major channel number is always the physical channel number associated with a broadcast frequency.
These two differing standards create a challenge for design of the digital television receiver. Since each format PSIP and MPEG uses its own Program Specific Information tables as defined in the respective specifications, the television receiver device must be able to distinguish between the two formats and use the Program Specific Information so that the receiver can receive both the PSIP and MPEG standard program formats in a manner which is transparent to the user.